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**Jim Cate** · 20-01-2019, 17:34

Chris,if 304/316 is "perfectly acceptable", why are so many folks here on CF having to replace chainplates on their boats?

Keeping the caulking on chainplates from leaking isn't so easy on many designs due to flexing, etc, and once leaking begins, the chance for oxygen deprivation on the plates is likely to follow and you know what that leads to!

My thought is that these days 2205 isn't all that expensive and in many designs not hard to fabricate, so why not use it? It's corrosion resistance is certainly better, and the additional strength is just a bonus.

The OPs convoluted plates are a worry! I'd be willing to notch the toe rails, etc, in order to get rid of the complex shapes, but that's a personal value set.

Jim

Wind River · 20-01-2019, 17:41

Quote:

Originally Posted by groundtackle

Wind River. That is unfortunate and after polishing all of them, surprised someone didn't spot it on the first one?.

I looked at them after polishing, the cracks were not there. They developed while they sat on my boat wrapped up for a year. You can even see small rust spots if you look closely. Those certainly would have been polished off.

It's a material quality control issue consistent with vessels from Taiwan and the area during that period. Kept me employed over the last 40 yrs replacing that metal. Using documented 304 / 316 above the waterline, polished, and properly installed is perfectly acceptable. Go 2205 if you like but strength or corrosion is not the issue. As fab ken say's.. when underwater and or additional strength required without without increasing dimension, like in your stainless Excel anchor shank. You also need some thickness for a good turnbuckle toggle fit.

So you believe this crevice corrosion I am seeing is not due to the stainless grade, but the quality of it?

Except... the main mast backstays if they split back at the mizzen outboard. Those fwd angles and loads were never taken into consideration on many Force 50 and Formosas etc small mizzen shared chainplates. I can't tell from pics if yours are done right. You also can't eliminate the bends on without taffrail interference.
Chris

Yes, the main has split back stays going to the forward pin of the aft chainplate.
What would you do for this? Have you ever heard of a failure do to this design?

groundtackle · 20-01-2019, 18:45

Jim, I haven't been following the threads but I have personally fabricated / replaced many chainplates and SS components with exactly the issues you describe. Water ingress is the concern that can be solved with proper installation but the method can be another complicated discussion. Every vessel/ item is a different but a solvable puzzle.
Back in the day you couldn't get 316 easily and stock dimensions were limited and expensive. Nowadays it's sometimes harder to find 304 and yes, 316 is preferred for an always trapped moisture situation. 304 is actually slightly stronger than 316 and more if using low carbon alloys for welding (316L).
You typically don't see a chainplate fail at the toggle hole unless it's poorly engineered or someone did some welding without good understanding or training. I have seen 2205 and many alloys fail in many applications like for example exhausts systems, grrrr.
So sure, go for the duplex if you like but just saying it's not required if properly installed, trust what alloy is used and welding must be performed using proper procedures. Just trying clarify that 304/316 can be used in many applications like this. This particular installation is difficult and maybe duplex would be better if it stays wet or can't basically stop the whole thing from moving with a better concept. WR is limited by factors that I don't like either.
Wind River, I guarantee the cracks were there and were missed unless you bent them after polishing. It takes an experienced eye as a polisher or maybe they didn't want to tell you for fear of loosing the polishing job.
I'd need to look closer but pretty sure that's just junk SS that may have been accelerated with corrosion of some kind. Is it everywhere or only on the the bends? it does happen in strange locations. I've seen so much of this and sometimes it won't show till you strike an arc with clean tig to watch the color and / or will open up a cavern right before your eyes. It's a welders worst nightmare and you put down the tools whenever discovered.
I'd like to spend a couple minutes with Mrs Groundtackle before we talk about your backstays. We leave for Seattle/ Vancouver boat shows so gone for 3 weeks and must give her the complete attention she deserves..
Chris

groundtackle · 20-01-2019, 22:46

Wind R, yes there have been failures. The main mast backstays can generate some serious loads and wood spars (if you still have them) is a heavy material. Chainplates need to be aligned parallel with the direction of load and sometimes they didn't do that for the backstays. The load just twists the undersized straps into line then bad things happen. Concentrate on getting those two chainplates lined up by overlapping straps or some other more complicated fabrication.
The standoffs or wood block spreaders under the chainplates are an issue. Perhaps another member can find the correct terminology because I don't know this one. I would treat that item in complete compression (if things are lined up), over bore the block, use a ss compression tube within and proper sized thru bolts inside that. Shorten them so the shrouds just clear taffrail. Its now just a beauty piece with some relative stability or when someone crashes you. They kinda sticky out.
Butyl is my preferred bedding compound in this case but its cold up here. That's another subject.
The eclipse is fantastic with a clear sky on southern van isle and everyone is happy.
Chris

Alan Mighty · 21-01-2019, 00:25

Quote:

Originally Posted by Wind River

Does anyone here have experience in fabricating with 2205 Stainless steel?
Specifically, experience in bending 1/2" thick 2205 plate.

I have been reading a lot about it, but it seems that there are many caveats that make me think twice about trying it myself. If this were just mild steel, I would either heat it up and bend it or put it in my press and bend it.

In reading about 2205, there is a very specific temperature range it needs to be in for hot bending and cold bending requires a much bigger bending radius than I have room for. It is said the minimum radius is twice the thickness of the piece being bent. I suppose I could modify the support the chain plate attaches too to allow for a bigger radius if need be.

Hot bending would allow me a tighter and much more controlled bend, as the spring back of this alloy is huge when bending cold. The graphs show a 45 degree bend will require about 60 degrees of bending to allow for spring back but is this the same for any thickness of material?

If hot bending, I would just heat the immediate area of the bend and not the entire plate. If I understand correctly, I would have to send out the entire piece to have it anneald afterwards for it to retain its strength and anti corrosive properties, adding to the cost.

Wind River: Hi!

Four years back I had external chainplates fabricated from 2205 (and a couple from 2504) duplex ss.

My vessel has three pairs of shroud chainplates, each with relaxed-Z bends not unlike yours. The big difference between my case and yours is the scantling: my plates were only 0.25" thick, half the thickness of yours.

I went to my local metal supplier who had the plate laser-cut to spec (including laser cutting square holes for the carriage bolts). And then to a local fabricator that is experience working with 2205 and 2504 duplex. I had done my research and knew about the springback issue. That fabricator was quite familiar with the issue. Cold press. No problem.

Four years later, I'm totally happy with my duplex ss chainplates.

To go back a para or two: like the chainplates in your photos, my chainplates had square holes to accommodate carriage bolts (square necked round head bolts). My original chainplates were 316 ss. And several showed stress cracks associated with those square holes. I've an in-law who is a metallurgist (both academic and industrial, meaning he has both taught in university engineering courses and worked in industry including as a consultant). The metallurgist reckoned that the original holes were likely drilled and then filed square and that of course the corners act as stress risers. The greater strength of 2205 plus neatly laser-cut squares (with slightly rounded corners) should be the solution.

To go overboard and ensure that I'd never worry about stress crack corrosion or crevice corrosion again, I also had carriage bolts and nuts carved from 2504 duplex (ain't no point fastening 2205 duplex plates to the hull with 316 ss bolts). The same mob that made the carriage bolts and nuts could have supplied them in 2205, but I followed the rule that bolts should be a superior grade to the chainplates (wrt to crevice corrosion and stress crack corrosion).

The firms I used are of course in Aus, so not relevant to you - except I suspect that the bolts were actually carved in a Scandinavian economy (you could probably get them done less expensively in China, of course).

My only advice therefore is to look for a fabricator who deals with 2205 duplex.

Wind River · 21-01-2019, 08:04

I think I am really stuck on the idea of using a better material than 304/316 Stainless for the chainplates. I think the limited additional cost is worth the improvement it provides.

The next issue is improving on the design without making too much impact on the aesthetics of the boat. I cant see adding a strap to the main mast backstay without it being a real eye soar. It seems to me the main problem with this design is the potential twist in the distance from the uppermost attaching bolt to the hull to the stays.

What do you think of this idea. Add about 1-1/4" of material to the rearward edge of the chainplate (red in the picture). This will act as a flange to bolt a gusset to that will bolt to the bulwark with a backing plate on the opposite side (gusset in blue).

This should not complicate too much an already complicated chainplate or ad additional stress to it.

Or, still add some more width to the rearward eadge of the chainplate and add two substantial bolts to the area going all the way through the bulwark and change the wood block to something like G10. Custom angled washers under the heads of the bolts. With this I think I can get rid of the 9" long 1/4" bolts through the toe rail. This seems to be the simplest approach to improving this design. Maybe not ideal, but improved.

Thoughts?

groundtackle · 21-01-2019, 09:13

Wind River, I concur with premium material and it's not beyond any decent metal shop expertise as Alan Mighty states.
I was looking at old rigging books and found the proper terminology 'Channels'
So - are you planning to replace or repair the channels or are they in good shape?
Your solution will certainly help. Simple is usually better and cheaper so just thinking out loud.
Consider the compression as well as tension. If you can keep the entire chainplate glued to the hull at the channel bolts that should stop twist and the yank fwd. Those bolts and the blocking behind are the weak link. Hide a piece of SS square or unequal tube inboard and beef up the bolts.
Chris

Pauls · 21-01-2019, 09:49

Here is some engineering data on the differences between 316 and 2205:

316 has a yield strength of 30K PSI, an ultimate tensile strength of 60 to 75K. It has a PREN (that is a measurement of corrosion resistance) of 23.1

2205 has a yield strength of 65K PSI, an ultimate tensile strength of 90K. It has a PREN of 34.3

To summarize, 2205 is 2.16 times stronger than 316 yield strength, 1.2 times stronger ultimate tensile strength, and 1.5 times more corrosion resistance than 316. There is no contest as to which is a better chainplate material.

In addition, because the 2205 is stronger than the 316 original chainplates, you can make them thinner. Or if you use the same thickness the they will be super robust.

Regarding previous posts about square holes, this is really bad design. A square hole is a stress riser which concentrates stress at the hole corners. Don't do this.

Wind River · 21-01-2019, 11:42

Quote:

Originally Posted by Pauls

Here is some engineering data on the differences between 316 and 2205:

316 has a yield strength of 30K PSI, an ultimate tensile strength of 60 to 75K. It has a PREN (that is a measurement of corrosion resistance) of 23.1

2205 has a yield strength of 65K PSI, an ultimate tensile strength of 90K. It has a PREN of 34.3

To summarize, 2205 is 2.16 times stronger than 316 yield strength, 1.2 times stronger ultimate tensile strength, and 1.5 times more corrosion resistance than 316. There is no contest as to which is a better chainplate material.

In addition, because the 2205 is stronger than the 316 original chainplates, you can make them thinner. Or if you use the same thickness the they will be super robust.

Regarding previous posts about square holes, this is really bad design. A square hole is a stress riser which concentrates stress at the hole corners. Don't do this.

I like the ides of "super robust".

To add insult to injury in my chainplate saga..... Not only did I pay to have them polished before I knew thet were bad, I bought a $200 broach to make those square holes!

The reason I did that is that carriage bolts were the only 316 stainless steel bolts that had a very wide head on them. About 1/4" wider on each side of the shank. I felt that this would help carry the load around the square hole and give more surface area for sealant.

The original bolts were carriage bolts with the square machined off and a slot cut into the head. That seemed like more work than broaching 46 holes. I didn't like the look of either Socket button head bolts or hex head bolts but if this is really a bad idea than I will look into other options.

Unfortunately for me, I also have already purchased the 316 stainless carriage bolts and had the heads polished for the original stainless chainplates.

There doesn't appear to be many options for 2205 bolts.

What are the thoughts of slightly rounding the corners of the square holes as Alan Almighty did? Seems like a reasonable solution coupled with the stronger material.

**a64pilot** · 21-01-2019, 12:50

If it’s a properly sized hole, you can fit a carriage bolt into a round hole.
Of course it’s not going to provide as much force to prevent rotation, but you may be surprised at how well it works.
Of course you could also use a an internal wrenching pan head bolt. They look nice and do not require a square hole.
I would go the internal wrenching bolt, but I’d also modify that wood work to get a flat plate.

Alan Mighty · 21-01-2019, 19:25

Quote:

Originally Posted by Wind River

There doesn't appear to be many options for 2205 bolts.

What are the thoughts of slightly rounding the corners of the square holes as Alan Almighty did? Seems like a reasonable solution coupled with the stronger material.

If'n you cannot find bolts in 2205 duplex ss in North America, with an economy more than 10 times larger than that in Australia, something be right wrong! You need to change your internet search provider. Or find a dead tree copy of Yellow Pages.

I'se on a passage at the moment and away from my documentation. My first mate done point out that I had uttered an error: I had my chainplate bolts and nuts whittled from 2507 superduplex ss, not 2504.

Seems as like 2507 superduplex ss is immune from crevice corrosion due to chloride ions unless the planet reach a temperature way above that suitable for intelligent life. As if there be any - intelligent life, that is - here now.

I would recommend you sell your crevice-corrosion prone, pasty-weak 316 austenitic ss bolts on eBay or suchlike and mosey down to your local fastenings shop to ante up for either 2205 duplex or 2507 super duplex ss bolts.

No point building in a weak link, prone to crevice corrosion, that can sit just where oxygen supply is scant when you've spent money on 2205 duplex plates.

Thet's what I did. I printed out a copy of an ASME bulletin (on ASME B18.5 round head square neck bolts) and walked into my local fastenings shop with the specs for what I wanted (diameter, length).

Thet good ol'boy what writes under the nom d'forum 'groundtackle' sed right: you're talking about a "channel" or "chain wale", about which your chainplate deviates. Not a "toerail'. The function of a channel is to spread the base of the triangle made by a stay or shroud (as hypotenuse), the mast (as the long side), and the deck (as the horizontal side) for your advantage.

As for removing the sharp corner of a square hole, operator of a laser cutter does that handily. No stress on the material when cutting the hole. And the radius-ing of the corner smooths away the stress riser.

Alan Mighty · 21-01-2019, 19:51

Quote:

Originally Posted by Alan Mighty

I would recommend you sell your crevice-corrosion prone, pasty-weak 316 austenitic ss bolts on eBay or suchlike and mosey down to your local fastenings shop to ante up for either 2205 duplex or 2507 super duplex ss bolts.

The big reliable source for 2507 superduplex ss is of course Sandvik. See: https://www.materials.sandvik/en/mat...dvik-saf-2507/

I'd be right surprised if cannot find a fastener shop around San Diego who works with 2507. I guess that the USN uses 2205 duplex and 2507 superduplex ss.

And if all else fails, you could talk to Nickel Systems over in Penn State. See: https://www.nickel-systems.com/mater...507-fasteners/

**Jim Cate** · 21-01-2019, 20:12

I must agree with Alan that use of a better grade bolt is indicated. And with no personal insult meant, predicating the choice of carriage head fasteners because of appearance favoritism over button head socket screws seems a poor value judgement. Even if you don't like their appearance (and FWIW I do like them), if you can get a better grade in the button heads they seem to be the right choice... and being able to simply drill round holes will save some money and for sure eliminate the stress risers associated with square holes (even with radiused corners).

Jim